Use of nonlinear pulsed magnetic fields for spatial encoding in magnetic resonance imaging.

This study examines the use of nonlinear magnetic field coils for spatial encoding in magnetic resonance imaging. Existing theories on imaging with such coils share a complex reconstruction process that originates from a suboptimal signal interpretation in the spatial-frequency domain (k-space). In this study, a new solution to this problem is proposed, namely a two-step reconstruction process, in which in the first step, the image signal is converted into a frequency spectrum, and in the second step, the spectrum, which represents the distorted image, is geometrically and intensity corrected to obtain an undistorted image. This theory has been verified by numerical simulations and experimentally using a straight wire as a coil model for an extremely nonlinear magnetic field. The results of this study facilitate the use of simple encoding coil designs that can feature low inductance, allowing for much faster switching times and higher magnetic field gradients.

In vivo continuous three-dimensional magnetic resonance microscopy: a study of metamorphosis in Carniolan worker honey bees (Apis mellifera carnica).

Three-dimensional (3D) magnetic resonance microscopy (MRM) is a modality of magnetic resonance imaging (MRI) optimized for the best resolution. Metamorphosis of the Carniolan worker honey bee (Apis mellifera carnica) was studied in vivo under controlled temperature and humidity conditions from sealed larvae until the emergence of an adult. The 3D images were analyzed by volume rendering and segmentation, enabling the analysis of the body, tracheal system and gastrointestinal tract through the time course of volume changes. Fat content sensitivity enabled the analysis of flight muscles transformation during the metamorphosis by the signal histogram and gray level co-occurrence matrix (GLCM). Although the transformation during metamorphosis is well known, MRM enables an alternative insight to this process, i.e. 3D in vivo, which has relatively high spatial and temporal resolutions. The developed methodology can easily be adapted for studying the metamorphosis of other insects or any other incremental biological process on a similar spatial and temporal scale.